1. Field of the Invention
The present invention relates to a traffic control apparatus for use with a frame relay communication and so forth.
2. Description of the Related Art
In recent years, a frame relay communication method that reduces a frame transfer time of a conventional packet switching unit has become popular. In the frame relay communication method, since an acknowledge operation of an information transfer made between subscriber terminals and the network, a retransmission control upon an occurrence of an error, and so forth, are performed by a sending subscriber terminal and a receiving subscriber terminal, the communication control of the network can be dramatically simplified. Thus, a high speed frame communication can be accomplished.
When a frame relay communication is executed, a physical channel (PLN) on which at least one time slot timing of a PCM line is allocated, is defined between a sending subscriber terminal and a receiving subscriber terminal. In addition, a plurality of data links that use the PLN are defined. When a subscriber uses the data link, he can communicate multiplexed information comprised of a plurality of types of data with a remote subscriber on one PLN. On the PLN, information is transmitted with a data unit that is referred to as a frame. The frame is composed of a header portion and an information portion. In the information portion of the frame, communication information is placed. In the header portion of the frame, a data link connection identifier (DLCI) that represents the relationship between communication information placed in the information portion of the frame and a data link, is placed.
In the network, a frame relay node unit that controls the frame relay communication is provided. The frame relay node unit identifies the timing of a time slot in which the frame is placed so as to identify the PLN of the frame. In addition, the frame relay node unit identifies the DLCI placed in the header portion of the frame so as to identify the data link of the frame. In this case, the frame relay node unit executes a traffic control (that is referred to as a committed information rate (CIR) control) for each data link of each PLN. Generally, the CIR control is a control method based on a traffic control method that is referred to as the Leaky Bucket method. Parameters and meanings used in the CIR method are as follows.
1. CIR (Committed Information Rate)
Transfer bit rate between a subscriber terminal and a frame relay node unit in a normal transfer state.
2. EIR (Excess Information Rate)
Transfer bit rate between a subscriber terminal and a frame relay node in a burst transfer state.
3. BC (Committed Burst Size)
Transfer data amount per unit period (Tc) at CIR.
4. BE (Excess Burst Rate)
Transfer data amount per unit period (Tc) at EIR.
5. CB (Committed Burst)
Remaining data amount transmittable by a subscriber terminal in each period .DELTA.T under the CIR control in the normal transfer state (packets).
6. EB (Excess Burst)
Remaining data amount transmittable by a subscriber terminal in each period .DELTA.T under the CIR control in the burst transfer state (bursts).
7. CIR.DELTA.T
Data amount supplied in a CB per period .DELTA.T under the CIR control in the normal transfer state. CIR.DELTA.T is equivalent to CIR.times..DELTA.T.
8. EIR.DELTA.T
Data amount supplied in an EB at each period .DELTA.T under the CIR control in the burst transfer state. EIR.DELTA.T is equivalent to EIR.times..DELTA.T.
When a data link is established, a subscriber contracts parameters BC and BE with a network provider. As described above, the parameter BC represents the data amount transferred between the subscriber terminal and a frame relay node unit per unit period (Tc) using the data link in the normal transfer state. On the other hand, the parameter BE represents the data amount transferred between the subscriber terminal and the frame relay node in the unit period (Tc) using the data link in the burst transfer state. The normal transfer state represents a period at which information is regularly transferred (normal communication state). The burst transfer state represents a period at which a large amount of information (such as image data) is instantaneously transmitted. The parameters BC and BE that are contracted amounts are equivalent to the transfer bit rates CIR and EIR, respectively. The frame relay node unit allocates a DLCI to the established data link, a buffer to DLCI, and various parameters including the BC and BE of the subscriber to the buffer.
When the frame relay node unit starts a frame relay communication corresponding to a set of a PLN and a DLCI, it designates the contracted amount BC corresponding to the PLN and the DLCI to a parameter CB that represents the remaining data amount in the unit period (Tc) in the normal transfer state. In addition, the frame relay node unit designates the contracted amount BE to a parameter EB that represents the remaining data amount per unit period (Tc) corresponding to PLN and DLCI. The frame relay node unit determines the PLN on which a frame has been received and the DLCI placed in the header portion of the frame so as to execute the CIR control for each PLN and each data link (DLCI).
When the frame relay node unit receives a frame, it subtracts the data amount of the frame from the value of the CB corresponding to the PLN and the DLCI of the frame. This process is executed until the value of the CB corresponding to the PLN and the DLCI is equal to or less than 0 whenever a frame is received. While the condition of 0&lt;CB.ltoreq.BC is satisfied, the data amount of the subscriber terminal using the PLN and the DLCI does not exceed the contracted amount in the normal transfer state.
When the value of the CB is equal to or less than 0 for each PLN and each DLCI, the data amount thereof exceeds the contracted amount in the normal transfer state. When the frame relay node unit further receives a frame corresponding to the PLN and the DLCI in the condition that CB.ltoreq.0, it sets a flag to the DE bit of the frame. In addition, the frame relay node unit subtracts the data amount of the frame from the value of the EB corresponding to the PLN and the DLCI thereof. Whenever the frame relay node unit receives a frame, it executes this process until the condition of EB.ltoreq.0 corresponding to the PLN and the DLCI of the frame is satisfied. While the relation of 0&lt;EB.ltoreq.BE for each PLN and each DLCI is satisfied, the data amount of the subscriber terminal that uses the PLN and the DLCI does not exceed the contracted amount in the burst transfer state.
When the value of the EB for each PLN and each DLCI is equal to or less than 0, the data amounts of the PLN and the DLCI exceed the contracted amounts in the burst transfer state. When the frame relay node unit further receives a frame corresponding to the PLN and the DLCI of which EB.ltoreq.0, it does not transfer the frame to the network, but discards it. The frame relay node unit determines the values of the CB and the EB, which are the remaining data amounts that the subscriber terminal can transmit in the normal transfer state and the burst transfer state, corresponding to the contracted amounts BC and BE per unit period (Tc). Thus, the values (contents) of the CB and the EB that are data packets should be supplied (compensated) at least every unit period (Tc). In practice, the frame relay node unit supplies supply data amounts CIR.DELTA.T and EIR.DELTA.T corresponding to each PLN and each DLCI to the values of the CB and the EB thereof every period .DELTA.T that is shorter than the unit period (Tc). As a result, when the values of the CB and the EB exceed the values of the BC and the BE corresponding thereto, the values of the CB and the EB are set to BC and BE (in full state), respectively.
However, in such a supplying process, the following problem will take place. The frame relay node unit may process a large number of PLNs and DLCIs. Conventionally, the frame relay node unitexecutes a supplying process for CBs and EBs corresponding to PLNs and DLCIs in each period .DELTA.T. Thus, when the number of PLNs and DLCIs are large, the frame relay node unit should concentratively execute the process in each period .DELTA.T. Consequently, the other processes of the CIR controlling processor of the frame relay node unit are delayed. As a result, the CIR controlling process is also delayed.
On the other hand, the process performance of the frame relay node unit depends on the process time for one frame. In other words, the process performance of the frame relay node unit accords with the number of frames that can be processed per unit period. Thus, when frames that exceed the process performance of the frame relay node unit are input, a so-called congestion control should be performed. On the other hand, in the frame relay node unit, the above-described CIR control should be executed. However, a control method for cooperatively and effectively executing the congestion control and the CIR control is not known in the frame relay communication method.
In addition, the frame relay node unit should perform various processes such as the CIR control and the congestion control along with the frame sending and receiving process, and the efficiency of the frame sending and receiving processes should be considered.
The above-mentioned problems are not limited to the frame relay communication method. Instead, these problems may happen in other communication methods.